Powered hot water heaters used for zone heating and for heating potable water are, of course, known. Such heaters utilize a fuel to allow a combustion engine to generate heat which heat is exchanged within a heat exchanger to a potable water circuit which is used for personal use by the occupants of a vehicle or boat. In addition to the combustion engine, there may also be an auxiliary heater used for supplying heated fluid to the potable water circuit when the engine is shut down and which auxiliary heater may supplement the generation of heat by the engine when the engine is operating if required.
There are disadvantages inherent in existing burners and heaters. One disadvantage is that the auxiliary heater is frequently operated to maintain the potable water in the potable water heating circuit at a desired operating temperature. This operation creates undesirable noise to which the occupants of the boat or vehicle are subjected.
A further disadvantage with existing burners and heaters is that a plurality of heat exchangers may be required for the various fluid circuits, namely the auxiliary heater primary heating loop, the vehicle engine heating loop and the potable water loop. Heat exchangers are expensive and it is desirable to reduce the hardware necessary for heat exchange between the various loops thereby reducing the manufacturing costs.
Yet a further disadvantage of existing heaters lies in the coolant jacket surrounding the burner. The auxiliary heater acts as a pressure vessel and the fluid within the coolant jacket is heated. This creates a rise in pressure due to the closed loop type system used for the coolant circuit. The fluctuations in pressure create a fluctuating force on the wall of the coolant jacket which, over time, causes fluctuating wall deflection which is associated with fatigue failure. It is desirable to minimize the pressure fluctuations in the coolant jacket and apply a more even force throughout the jacket walls which will thereby extend the life of the coolant jacket surrounding the burner.
Yet a further disadvantage of existing heater systems lies in the heating of the potable water used in the system. Heretofore, the auxiliary heater was turned on to heat water when the potable water temperature decreased to a predetermined value which was sensed by a control system which, in turn, initiated operation of the auxiliary heater. This, however, resulted in significant temperature differences at the tap which is uncomfortable for users.
Yet a further disadvantage with existing heater systems is that the heating system must initially be filled with coolant and the embedded air within the system must be purged. These operations necessarily take a good deal of time to ensure the integrity of the coolant filling and pressure testing operations.